Thanks for posting your experience its very useful sharing such things for the other ppl planning to buy such stuff, as a thank you I will post my experience
I bought a single band antenna of asus themselve the link below here
http://www.amazon.com/dp/B0046HQKV6/?tag=snbforums-20
I have not seen any improvement in the 2.4Ghz infact it was worse, and one day while reading I think one of toastmaster articles about antenna I learned that those high gain antenna,s only have an positive effect when going horizontal meaning at the same floor, vertical signal will decrease so between floors it becomes weaker. Anyway it was a good read, and my test though unsuccessful was still a joy for me crossing down oan "IF" out of my mind
What I learned is that the 2dbi antenna is 360 degree, which means the vertical direction has the same signal as horizontal direction. but the antenna has short range.